The present invention relates to the manufacture of smart cards, and more particularly cards capable of functioning without contact by means of an antenna integrated into the card.
Such cards are intended for performing various operations such as, for example, banking operations, telephone communications, identification operations, operations of debiting or recharging units of account, and all kinds of operations which can be performed remotely by high-frequency electromagnetic coupling between a transmission/reception terminal and a card placed in the area of action of this terminal.
One of the main problems which it is necessary to resolve in the manufacture of such cards is the connection of the antenna to the integrated-circuit chip which provides the electronic functioning of the card. Another problem which it is necessary to resolve is the reduction of the thickness of the card as far as possible. The conventional constraints of mechanical strength, reliability and manufacturing cost must obviously be taken into account in this manufacture.
A known solution from the prior art, described in the document PCT WO 96/07985, for effecting the connection between the antenna and the integrated-circuit chip, consists of forming metallic protrusions on two contact pads on the chip, and then connecting these protrusions to the ends of an antenna wire. In this case, the antenna wire is a copper wire formed on a substrate and the protrusions are applied to this antenna wire by hot compression.
However, the interconnection unit thus obtained has problems of mechanical strength and tensile fragility of the connection. This is because, when the chip is subjected to mechanical stresses, the protrusions suffer damage affecting the quality of the electrical connection. The mechanical stresses can even go as far as causing the rupture of the protrusions and consequently the pulling away of the chip. The contactless smart cards produced according to this prior method therefore have a relatively short service life.
In another known solution from the prior art, the connection between the antenna and the chip is effected by means of conductive glue applied between the antenna and metallic protrusions formed on two contact pads on the chip. In this case, however, a significant excess thickness appears because of the presence of the glue and the protrusions. In addition, the manufacture of the card requires an additional step of dispensing the dots of glue.
The protrusions, and where applicable the dots of conductive glue, have a not insignificant thickness which is added to that of the antenna and that of the chip, which increases the bulk of the interconnection unit obtained. However, it is sought to obtain an interconnection unit of very small size in order to produce an ultraflat contactless smart card, that is to say with a thickness less than the standard ISO thickness.